This invention relates to the field of semiconductor electro-optic devices. The present invention is intended to be used in areas such as telecommunications, optical signal processing, scanning and displays.
Standard designs for polarization insensitive semiconductor modulators that use uniform tensile strained quantum wells have limited insensitivity. They are only insensitive at particular applied voltages. This is important to note since modulators are bias dependent devices. Modification of the quantum well structure in these semiconductor modulators changes the optoelectronic properties of these modulators. Moreover, modification of the band structure, in particular, in semiconductor quantum wells can lead to significant improvement in the performance of many semiconductor optoelectronic devices. The electric field within the quantum wells plays a significant role in changing the optical properties of semiconductor waveguide modulators. Quantum well structures exhibit a large field induced refractive index and absorption change due to the Quantum Confined Stark Effect (QCSE). Performance of optical switches and modulators depend upon the properties of the semiconductor quantum well structures.
The properties achieved by modifying the band structure in semiconductor quantum wells can make semiconductor quantum well waveguide switches/modulators polarization dependent. This, polarization dependence, is an undesirable property in optical communication applications where polarization preserving optical fiber cannot be used. Therefore, a polarization insensitive/independent semiconductor waveguide switch/modulator is desirable.
It has been suggested in the art that polarization insensitivity can be achieved in quantum well structures by merging the first heavy hole (HH) subband and the first light hole (LH) subband in a uniformly tensile strained quantum well. In this case, polarization independence can be achieved at a particular bias. It has also been suggested in the prior art that tensile strained barriers can produce similar results.
Although it has been suggested that polarization insensitive properties can be achieved in a tensile strained quantum well, to date, these properties are bias dependent. This is due to the fact that the first HH subband and first LH subband have different sensitivities to the QCSE.
The need exists for the fabrication and design of true polarization insensitive/independent semiconductor waveguide modulators that are insensitive to bias variations at any chosen wavelength. The present invention provides for these true polarization insensitive/independent semiconductor waveguide modulators that have greater utility and insensitivity. The invention allows the semiconductor waveguide modulator to be insensitive to bias variations. The unique bias independent polarization properties of the present invention have important applications in optoelectronic devices.